1. Field of the Invention
The present invention relates to a structure of a vibration wave motor driven by a travelling vibration wave, and more particularly to a support structure of a vibration member of the vibration wave motor.
2. Description of the Prior Art
A vibration wave motor transduces a vibration motion created by application of a periodic voltage to electrostrictive elements to a rotational motion or a linear motion. Because it does not require windings as opposed to a conventional electromagnetic motor, it is simpler and smaller in structure and produces a high torque at a low rotating speed.
FIGS. 1 and 2 show the principle of how such devices are driven numerals 2a and 2b denote elecrostrictive elements which are bonded or welded to the vibration number 1 (usually made of metal) and arranged on one side of the vibration member 1 with a spatial phase difference of .lambda./4 therebetween.
The vibration member 1 is used as one electrode for the electrostrictive elements 2a and 2b and an A.C. voltage V=Vo sin .omega.t is applied to the electrostrictive element 2a from an A.C. power supply 3a while an A.C. voltage V=Vo sin (.omega.t.+-..pi./2) having a phase difference of .lambda./4 is applied to the electrostrictive element 2b, where signs + and - are selected by a phase shifter 3b in accordance with a direction of movement of the movable member 5. Let us assume that the sign - is selected and the voltage V=Vo sin (.omega.t-.pi./2) is applied to the electrostrictive element 2b.
When only the electrostrictive element 2a is vibrated by the voltae V=Vo sin .omega.t, a vibration by a standing wave is generated as shown in FIG. 1(a), and when only the electrostrictive elements 2b is vibrated by the voltage V+Vo sin (.omega.t-.pi./2), a vibration by a standing wave is generated as shown in FIG. 1(b). When the two A.C. voltages having the phase difference therebetween are simultaneously applied to the electrostrictive elements 2a and 2b, the surface wave travels.
FIGS. 1(A), 1(B), 1(C) and 1(D) show the surface waves at times t=2n.pi./.omega., +2n.pi./.omega., t=.pi./.omega.+2n.pi./.omega. and t=3.pi./2.omega.+2n.pi./.omega., respectively, and the wavefront travels in x-direction.
Such a travelling surface wave includes a longitudinal wave and a lateral wave. Looking at a mass point A of the vibration member 1 as shown in FIG. 2, a longitudinal amplitude u and a lateral amplitude w make a rotating elliptic motion.
A movable member 5 is press-contacted to the surface of the vibration member 1 and it makes contact with only an apex of the vibration member. (Actually, it makes contact with an area having a definite width.) Accordingly, the vibration member 5 is driven by the longitudinal amplitude component u of the elliptic motion of the mass points A, A', . . . at the apex and it moves in an arrow direction N.
When the phase of the voltage is shifted 90.degree. by the 90.degree. phase shifter, the surface wave travels in -x direction and the movable member 5 moves in the opposite direction to the direction N.
The velocity of the mass point A at the apex is V=2.pi.fu (where f is a vibration frequency) and the velocity of the movable member 5 depends thereon and also depends on the lateral amplitude w because of the frictional drive by the press-contact.
The velocity of the movable member 5 is proportional to the magnitude of the elliptic motion of the mass point A and the magnitude of the elliptic motion is proportional to the voltage applied to the electrostrictive elements. The magnitude of the elliptic motion is also proportional to the areas of the electrostrictive elements 2.
It is difficult to support the vibration member 1 without impeding its vibration. In the past, it was supported by felt material. However, when soft material such as felt is used, it is difficult to precisely position the vibration member 1 and the material is deteriorated by aging.
In order to resolve the above problem with the motor packaging, a support device which uses an auxiliary vibration member has been proposed by the assignee of the present application in co-pending U.S. Ser. No. 663,144 filed on Oct. 22, 1984, now abandoned. However, since a ring-shaped vibration member in the proposed device requires accurate length and width in shape and accurate weight in mass, it is usually difficult and expensive to form the auxiliary vibration member projecting from the ring-shaped vibration member in union with the ring-shaped vibration member.